守權

A defender who advances to the outer walls to intercept or retreats to outposts and watchtowers to fight is not a skilled defender. Concentrating all the brave warriors, strong armor, sharp weapons, powerful crossbows, and sturdy arrows inside the inner walls, withdrawing stores from outlying granaries, demolishing suburbs and bringing everything into the citadel -- this hands the attacker ten to a hundred times the morale advantage while the defender retains less than half. The attacker suffers greatly from this. Yet ordinary generals do not understand this principle.

Defense means not losing your strongpoints. The rule of defense: for every ten feet of wall, station ten men -- not counting engineers and supply personnel. Those who sortie do not defend; those who defend do not sortie. One defender counters ten attackers; ten counter a hundred; a hundred counter a thousand; a thousand counter ten thousand.

Therefore building city walls is not merely an expense of labor and earth -- it exists precisely for defense. A city with a thousand feet of wall requires ten thousand defenders. Deep and wide moats, solid and thick walls, fully equipped soldiers and civilians, adequate fuel and food supplies, sturdy crossbows and strong arrows, matched with spears and halberds -- this is the method of defense.

An attacker needs at least a hundred thousand troops. Where there is a guaranteed relief force, there is a city that can be held. Where there is no guaranteed relief force, there is no city that can be held.

If the walls are strong and relief is truly coming, then even ordinary men and women will shield the walls with their bodies and pour out every resource in bloody defense. A city under year-long siege can outlast its attackers if the defenders outlast through belief in relief.

But if the walls are strong yet relief is not genuinely coming, then even ordinary men and women will hide in the shadows weeping -- this is human nature. Once people reach this state, even if you open the granaries and distribute supplies to reassure them, you cannot stop the collapse.

Therefore, place the brave warriors with strong armor, sharp weapons, powerful crossbows, and sturdy arrows at the front, and station the weak and infirm at the rear.

When a hundred thousand enemy troops are encamped beneath the walls, the relief force must break through to them, and the garrison must sortie to link up. Move out to seize key positions, protect the rear, and keep supply lines open. Coordinate between forces inside and outside the city.

If the relief force merely makes a show of coming without genuine commitment -- displaying insincerity -- then the enemy will simply turn and wait for the relief force to exhaust itself. If you put the strong in the rear and the old in front, the enemy will face no real threat ahead, and the garrison cannot hold.

This is what is meant by the principles of defense.